IDENTIFICATION AND PROPERTIES OF RENAL MINERALOCORTICOID RECEPTORS IN RELATION TO GLUCOCORTICOID BINDERS IN RAT-LIVER AND KIDNEY

The binding of the natural mineralocorticoid aldosterone and the glucocorticoid corticosterone to macromolecules in rat liver and kidney cytoplasmic fractions was compared by various chromatographic procedures. Equilibration of kidney cytosol with 10 nM-aldosterone, either alone or in the presence of a competing steroid, was ideal for ion-exchange chromatography on DEAE-cellulose DE-52, and revealed the presence of 4 sorts of binding components. One of these, eluted in the 0.001 M-phosphate pre-wash, and another, less abundant, forming a peak at 0.006 M-phosphate, did not bind corticosterone at equimolar concentrations, and appear to constitute the mineralocorticoid-specific MR receptor in rat kidney. They could not be detected in the liver. Radioactivity eluted in the 0.02 and 0.06 M-phosphate regions on DEAE-cellulose DE-52 appears to be due to [3H]aldosterone binding to glucocorticoid-specific GR receptors and to transcortin respectively, since labeling was greater with corticosterone even at 10 nM than with the mineralocorticoid at 100 nM and since [14C]corticosterone bound to blood serum transcortin was always co-chromatographed in the 0.06 M-phosphate region. These 2 components appear to be identical with those in the liver and could be labeled maximally only by 100 nM-corticosterone. The separation between specific mineralo- and gluco-corticoid-binding species was less clear when chromatography was attempted on DEAE-Sephadex A-50 columns, possibly because of disaggregation into subunits in the presence of the high KCl concentrations required for elution. Competitive binding followed by filtration through Sephadex G-200 gels indicated that cellular MR binders, unlike GR receptors, exist mostly as high-molecular-weight aggregates, although both appear to exhibit a comparable monomeric molecular weight of .apprxeq. 67,000.